Vacuum deposition is a common method for coating metals such as aluminum, copper, zinc, and tin onto various substrates of metal, glass and plastic. In the conventional vacuum deposition process a container is heated by electric resistance heating to vaporize metal in contact with the container. The container is commonly referred to as a "vaporization boat" or simply a "boat" and is connected in an electric circuit which a source of electrical power provides sufficient current flow directly through the boat to heat the boat to a temperature which will cause the metal in contact with the boat to vaporize. The electrical connection is accomplished using a clamp. The metal is vaporized in an evacuated atmosphere for coating a product which may be individually introduced into the evacuated chamber, or continuously fed through the chamber or, alternatively, may form part of the chamber itself. A wide variety of product is coated with metal using vapor deposition including, e.g., television picture tubes, automobile headlights, toys and the like.
Presently, most clamp systems are composed of a metal bar or bracket and a body assembly which are fastened about the ends of a boat using machine screws or bolts. Contact pressure on the boat is provided by tightening the bolts to draw the body and bar boat is provided by tightening the bolts to draw the body and bar assembly into tight engagement. To insure good electrical and mechanical contact the bolts are tightened aggressively so that there is little or no opportunity for the boat to move relative to the clamp. It has been discovered that this sets up a life degrading stress as a result of repeated thermal cycling of the boat in normal operation. In each cycle of operation the boat is resistance heated to a temperature to vaporize metal which causes the boat to expand. However upon cooldown at the end of each cycle the boat contracts. The present clamping mechanism does not allow for relative movement between the boat and the clamp.